Isabel, moral philosopher and amateur detective, living in McCall Smith’s Edenic Edinburgh, has plenty of time between investigations to ponder the pettiness of her neighbors and engage in self-introspection. The case demanding her expertise requires her to probe into the backgrounds of three candidates for a headmaster’s job at a local boys’ school, instigated by a mysterious anonymous letter. But Isabel’s investigations are secondary to her quotidian preoccupations. The series is charmingly narrated by Davina Porter, who has locked in her portrayals of Isabel, Jamie, and their son, Charlie. As usual, Porter settles on just the right tone for every newcomer. She provides McCall Smith fans with another dead-on performance worth lingering over. A Pantheon hardcover (Reviews, Aug. 16). (Oct.)